Organic thin-film solar cell and method of producing same

ABSTRACT

Providing an organic thin-film solar cell that can be easily manufactured and then mass produced at low cost while increasing the photoelectric conversion efficiency, and the method of producing the same. 
     Solar cells  100 - 102  include at least one of a mixed P-type organic semiconductor layer  12 M and a mixed N-type organic semiconductor layer  14 M. A plurality of organic semiconductor materials are mixed in the mixed P-type organic semiconductor layer  12 M or the mixed N-type organic semiconductor layer  14 M, respectively. In such a way, the photoelectric conversion efficiency of the solar cells is increased by selecting and mixing proper organic semiconductor materials to form the organic semiconductor layer.

TECHNICAL FIELD

The present invention relates to an organic thin-film solar cell, andparticularly relates to an organic thin-film solar cell including anorganic semiconductor layer utilizing a plurality of organicsemiconductor materials and a method of producing the same.

BACKGROUND ART

Various types of solar cells utilizing an organic semiconductor materialare known. The examples include a dye-sensitized solar cell utilizing aphotosensitization effect (for example, Patent Citations 1 and 2), andan organic thin-film solar cell having a tandem structure in which aplurality of semiconductor layers that are P-type or N-type doped andcomposed of a single material are stacked, respectively, (for example,Patent Citation 3), and so on.

Patent Citation 1: JAPANESE UNEXAMINED PATENT PUBLICATION (KOKAI)No.2000-195569

Patent Citation 2: JAPANESE UNEXAMINED PATENT PUBLICATION (KOKAI)No.2005-26051

Patent Citation 3: PUBLISHED PATENT APPLICATION, JAPANESE TRANSLATION OFPCT NATIONAL PUBLICATION OF THE

TRANSLATED VERSION (Laid-open) No. 2006-520533

DISCLOSURE OF INVENTION Technical Problem

In the manufacture of a dye-sensitized solar cell, it is necessary thata dye layer composed of a predetermined dye is formed and made into afilm, and then laminated on a semiconductor layer of titanium oxide andso on. Accordingly, it is difficult to manufacture the dye-sensitizedsolar cell with a simple manufacture process, and the structure of thecompleted dye-sensitized solar cell is complicated.

Further, in the organic thin-film solar cell having the tandemstructure, a plurality of semiconductor layers of which materials aredifferent from each other are laminated together to expand thesolar-light absorption region. However, since many organic semiconductorlayers are provided, it is difficult to select and stabilize anelectrode film that is laminated between the organic semiconductorlayers and the manufacturing process becomes complicated. Thecomplicated nature of the manufacturing process is a factor which raisesthe cost for manufacturing the organic thin-film solar cell having thetandem structure.

Therefore, the object of the present invention is to provide an organicthin-film solar cell that can be easily manufactured to enable massproduction at a low cost, while improving the photoelectric conversionefficiency, and the method of producing the same.

Technical Solution

An organic thin-film solar cell in the present invention comprises aP-type organic semiconductor layer and an N-type organic semiconductorlayer. The organic thin-film solar cell is characterized in that atleast one of the P-type organic semiconductor layer and N-type organicsemiconductor layer comprises a mixture of a plurality of organicsemiconductor materials of which absorption bands in the opticalabsorption spectrum are different from each other.

In the organic thin-film solar cell, it is preferable that a mixed layercomprising a mixture of a P-type organic semiconductor material and anN-type organic semiconductor material is further provided between theP-type organic semiconductor layer and the N-type organic semiconductorlayer. Furthermore, it is preferable that the organic thin-film solarcell further comprises an electrode and a buffer layer, wherein thebuffer layer is provided between the electrode and an organicsemiconductor layer of at least one of the P-type organic semiconductorlayer and the N-type organic semiconductor layer.

For example, the P-type organic semiconductor layer includespolyphenylene vinylene, polyphenylene vinylene derivative,polythiophene, phthalocyanine, phthalocyanine derivative, porphyrin,pentacene, or rubrene as the organic semiconductor material.Furthermore, the N-type organic semiconductor layer includes fullerene,fullerene derivative, carbon nanotube, or carbon nanotube derivative, asthe organic semiconductor material, for example. Further, in the organicthin-film solar cell, at least one of the P-type organic semiconductorlayer and the N-type organic semiconductor layer may be plurallystacked.

A method of producing an organic thin-film solar cell in the presentinvention is the method of producing the organic thin-film solar cellcomprising a P-type organic semiconductor layer and an N-type organicsemiconductor layer. The method of producing an organic thin-film solarcell in the present invention is characterized in that at least one ofthe P-type organic semiconductor layer and the N-type organicsemiconductor layer is formed by mixing a plurality of organicsemiconductor materials.

Advantageous Effects

The present invention can provide an organic thin-film solar cell whichcan be easily manufactured to enable mass production at a low cost whileimproving the photoelectric conversion efficiency, and method ofproducing the same.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-section view which schematically shows an organicthin-film solar cell of a first embodiment.

FIG. 2 is a cross-section view which schematically shows an organicthin-film solar cell including a mixed layer in the first embodiment.

FIG. 3 is a cross-section view which schematically shows an organicthin-film solar cell including a mixed layer in a second embodiment.

FIG. 4 is a cross-section view which schematically shows an organicthin-film solar cell of the second embodiment.

FIG. 5 is a view which shows the optical absorption spectrums of thestandalone semiconductor materials and a mixture thereof.

EXPLANATION OF REFERENCES

-   100-111 Solar Cell (Organic Thin-Film Solar Cell)-   12 P-type Organic Semiconductor Layer-   12M Mixed P-type Organic Semiconductor Layer-   14 N-type Organic Semiconductor Layer-   14M Mixed N-type Organic Semiconductor Layer-   20 Mixed Layer

Embodiments for Carrying out Invention

An organic thin-film solar cell in a first embodiment is explainedbelow. FIG. 1 is a cross-section view which schematically shows theorganic thin-film solar cell of the first embodiment. Furthermore, eachlayer composing the organic thin-layer solar cell is enlarged in thethickness direction in FIG. 1 and the following figures, for convenienceof explanation.

Solar cells 100-102 of this embodiment, which are the organic thin-filmsolar cells, include a P-type organic semiconductor layer 12 or 12M andan N-type organic semiconductor layer 14 or 14M. The P-type and N-typeorganic semiconductor layers 12, 14 and so on are provided between anelectrode 16 (anode) at the surface and a transparent electrode 18(cathode) on a substrate 15. Thus, in the solar cells 100-102 of thisembodiment, the transparent electrode 18 is provided on the substrate 15side, and the P-type organic semiconductor layer 12 or 12M, the N-typeorganic semiconductor layer 14 or 14M, and the electrode 16 are stackedthereon in this order. Hereinafter, the structure of the solar cells100-102 in this embodiment; namely, the structure in which the electrode16 is disposed at the surface on the opposite side of the substrate 15and the transparent electrode 18 is disposed on the substrate 15 side,will be called the “bottom-type”.

In this embodiment, a main component of at least one of the P-typeorganic semiconductor layer and the N-type organic semiconductor layeris a mixture of a plurality of organic semiconductor materials. Namely,the solar cells of this embodiment include the solar cell 100 that has amixed P-type organic semiconductor layer 12M that is formed by mixing aplurality of P-type organic semiconductor materials together in only theP-type organic semiconductor layer as shown in FIG. 1A; the solar cell101 that has a mixed N-type organic semiconductor layer 14M that isformed by mixing a plurality of N-type organic semiconductor materialstogether in only the N-type organic semiconductor layer as shown in FIG.1B; or the solar cell 102 that has the mixed P-type organicsemiconductor layer 12M that is formed by mixing a plurality of P-typeorganic semiconductor materials and the mixed N-type organicsemiconductor layer 14M that is formed by mixing a plurality of N-typeorganic semiconductor materials as shown in FIG. 1C.

In the solar cells 100-102, when light that is incident from thesubstrate 15 side as indicated by an arrow L reaches a contact facebetween the mixed P-type organic semiconductor layer 12M and the N-typeorganic semiconductor layer 14, between the P-type organic semiconductorlayer 12 and the mixed N-type organic semiconductor layer 14M, orbetween the mixed P-type organic semiconductor layer 12M and the mixedN-type organic semiconductor layer 14M, pairs of holes and electrons aregenerated. And then, the hole transfers to the P-type organicsemiconductor layer 12 or the mixed P-type organic semiconductor layer12M side and the electron transfers to the N-type organic semiconductorlayer 14 or the mixed N-type organic semiconductor layer 14M side, sothat the electric current flows.

The P-type organic semiconductor material included in the P-type organicsemiconductor layer is not particularly limited as long as the carrierthat produces the electric conduction is mainly hole, but polyphenylenevinylene (PPV); polyphenylene vinylene derivatives such aspoly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene](MDMO-PPV), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), and so on; polythiophene derivatives such aspoly-3-hexylthiophene (P3HT), poly-3-octylthiophene (P3OT),poly-3-dodecylthiophene (P3DDT), and so on; phthalocyanine;phthalocyanine derivatives such as copper phthalocyanine, zincphthalocyanine, titanyl Phthalocyanine, and soon; porphyrin; pentacene;and rubrene are preferable. The mixed P-type organic semiconductor layer12M is formed by mixing a plurality of organic semiconductor materials,selected from these P-type organic semiconductor materials, whoseabsorption bands in optical absorption spectrum are different from eachother. The P-type organic semiconductor layer 12 is formed by one ofthese P-type organic semiconductor materials. Further, the plurality ofP-type organic semiconductor materials included in the mixed P-typeorganic semiconductor layer 12M can be mixed at an arbitrary rate, but aP-type organic semiconductor material that represents the smallestportion included in such a layer is not less than 10 mol %, based on thetotal of the P-type organic semiconductor materials in the mixed P-typeorganic semiconductor layer 12M.

The N-type organic semiconductor material included in the N-type organicsemiconductor layer 14M is not particularly limited as long as thecarrier that produces the electric conduction is mainly electron, butfullerene, fullerene derivatives such as [6,6]-phenyl-C₆₁-butyric acidmethyl ester (PCBM), carbon nanotube, and carbon nanotube derivativesare preferable. The mixed N-type organic semiconductor layer 14M isformed by mixing a plurality of organic semiconductor materials,selected from these N-type organic semiconductor materials, whoseabsorption bands of the optical absorption spectrum are different fromeach other. The N-type organic semiconductor layer 14 is formed by oneof these P-type organic semiconductor materials. Further, the pluralityof N-type organic semiconductor materials included in the mixed N-typeorganic semiconductor layer 14M can be mixed at an arbitrary rate.

The thickness of the P-type organic semiconductor layer 12, the mixedP-type organic semiconductor layer 12M, the N-type organic semiconductorlayer 14, and the mixed N-type organic semiconductor layer 14M isgenerally from 5 to 500 nm, and is preferably from 10 to 100 nm.Further, as the substrate 15, the transparent electrode 18, andelectrode 16 that are utilized in this embodiment, the materials thatconstitute the known organic thin-film solar cell can be used. Examplesfor the substrate 15 include glass, synthetic resin film, and so on,which are transparent; examples for the electrode 16 include a filmcomposed of metal such as gold, silver, copper, aluminum, and so on; andexamples for the transparent electrode 18 include tin-doped indium oxide(ITO), tin oxide, zinc oxide, and so on.

The P-type and N-type organic semiconductor layers, or either one ofthese are formed by the mixture of a plurality of organic semiconductormaterials whose absorption bands in optical absorption spectrum aredifferent from each other, which can increase the photoelectricconversion efficiency of the solar cell as described below. Moreover,the structure of the solar cell is simpler in this embodiment, comparedto the case where it is intended to increase the photoelectricconversion efficiency with the tandem structure in which a P-typeorganic semiconductor layer including one P-type organic semiconductormaterial and an N-type organic semiconductor layer including one N-typeorganic semiconductor material are stacked in plural layers. The reasonis that the photoelectric conversion efficiency can be increased withonly two layers: the P-type organic semiconductor layer and the N-typeorganic semiconductor layer.

The bottom-type solar cell may be a solar cell 103 in which a mixedlayer 20 is provided between the mixed P-type organic semiconductorlayer 12M and the N-type organic semiconductor layer 14; a solar cell104 in which a mixed layer 20 is provided between the P-type organicsemiconductor layer 12 and the mixed N-type organic semiconductor layer14M; or a solar cell 105 in which a mixed layer 20 is provided betweenthe mixed P-type organic semiconductor layer 12M and the mixed N-typeorganic semiconductor layer 14M, as shown in FIGS. 2A-2C. Here, thesubstrate 15, the transparent electrode 18, the P-type organicsemiconductor layer 12, the mixed P-type organic semiconductor layer12M, the N-type organic semiconductor layer 14, the mixed N-type organicsemiconductor layer 14M, and the electrode 16 are similar to those inthe solar cells 100-102 described above. Further, in FIG. 2 and thefollowing, components which are the same or correspond to those in thesolar cells 100-102 of the first embodiment are labeled by the samereferences as in FIG. 1.

The mixed layer 20 includes a P-type organic semiconductor material andan N-type organic semiconductor material, and it is preferable that theP-type organic semiconductor material and the N-type organicsemiconductor material are mixed in equal amounts (molar number). As forthe P-type organic semiconductor material and the N-type organicsemiconductor material, one or a plurality of materials may be used.Further, in regard to the P-type organic semiconductor material and theN-type organic semiconductor material, materials similar to thosedescribed above can be used.

As described, the photoelectric conversion efficiency of the solar cellcan be increased by providing the mixed layer 20 between the (mixed)P-type organic semiconductor layer and the (mixed) N-type organicsemiconductor layer. The reason is that it can create the PN junctionbetween the P-type and N-type organic semiconductors on the molecularlevel in the mixed layer 20.

Moreover, a buffer layer (not shown in FIGS.) may be further stacked inthe bottom-type solar cells 100-105. The buffer layer is providedbetween an electrode and an organic semiconductor layer of at least oneof the P-type organic semiconductor layer and the N-type organicsemiconductor layer, but it is generally provided between the N-typeorganic semiconductor layer 14 or the mixed N-type organic semiconductorlayer 14M and the electrode 16, and between the P-type organicsemiconductor layer 12 or the mixed P-type organic semiconductor layer12M and the transparent electrode 18.

Examples of the buffer layer that is provided between the N-type organicsemiconductor layer 14 and the electrode 16 or between the mixed N-typeorganic semiconductor layer 14M and the electrode 16 include BCP(bathocuproine; 2,9-dimetyl-4,7-diphenyl-1,10-phenanthroline), which isas a hole-blocking material. Examples of the buffer layer that isprovided between the P-type organic semiconductor layer 12 and thetransparent electrode 18 or between the mixed P-type organicsemiconductor layer 12M and the transparent electrode include PEDOT:PSS(a complex of poly(3,4-ethylenedioxythiophene) andpoly(4-styrenesulfonate)), MoO₃ (molybdenum trioxide), and so on. Theperformance of the solar cells 100-105 can be further improved byproviding such a buffer layer.

Further, both the mixed layer 20 described above (refer to FIGS. 2A-2C)and the buffer layer (not shown in FIGS.) may be provided in thebottom-type solar cells 100-105. In this case, both of theabove-mentioned effects that are produced by the mixed layer 20 andbuffer layer can be obtained.

The method of producing the solar cells 100-105 is not particularlylimited, but the solar cell can be produced by laminating thetransparent electrode 18, the mixed P-type organic semiconductor layer12M, the P-type organic semiconductor layer 12, the mixed N-type organicsemiconductor layer 14M, the N-type organic semiconductor layer 14, theelectrode 16, the mixed layer 20, the buffer layer and/or others, on thesubstrate 15 in accordance with the intended structure of the solarcell, for example. The method of lamination is appropriately selecteddepending on the laminated material. For example, the electrode 16 andthe transparent electrode 18 can be formed by vacuum deposition,sputtering, or others. The mixed P-type organic semiconductor layer 12M,the P-type organic semiconductor layer 12, the mixed N-type organicsemiconductor layer 14M, the N-type organic semiconductor layer 14, themixed layer 20, and the buffer layer can be formed by vacuum deposition,spin coating, or others. For forming the mixed P-type organicsemiconductor layer 12M, the mixed N-type organic semiconductor layer14M and the mixed layer 20, co-evaporation, or spin coating using asolution including two or more kinds of materials may be done. Further,after laminating, sealing by a glass cap and so on is preferred in orderto prevent degradation from moisture and so on.

Next, an organic thin-film solar cell in a second embodiment, mainly thedifferences from that in the first embodiment, will be explained. FIG. 3is a cross-section view which schematically shows the organic thin-filmsolar cells 106-108 of the second embodiment.

The organic thin-film solar cells 106-108 of the second embodiment havea structure wherein the electrode 16 is disposed on the substrate 15side and the transparent electrode 18 is disposed at the surface on theopposite side of the substrate 15, and the light L is incident from thetransparent electrode 18 side. Hereinafter, such a structure of thesolar cells 106-108 in this embodiment is called the “top-type”. Asshown in FIGS. 3A-3C, in the solar cells 106-108 of this embodiment, atleast one of the mixed P-type organic semiconductor layer 12M and themixed N-type organic semiconductor layer 14M is provided also.

Accordingly, the photoelectric conversion efficiency of the solar cellin this embodiment can also be increased. Furthermore, the top-typesolar cells 106-108, in which the arrangement of the layer members isthe only difference from the structure of the bottom-type, have a simplestructure similar to the bottom-type.

Also in the top-type solar cell, the mixed layer 20 may be furtherstacked between the mixed P-type organic semiconductor layer 12M and theN-type organic semiconductor layer 14, between the P-type organicsemiconductor layer 12 and the mixed N-type organic semiconductor layer14M, and between the mixed P-type organic semiconductor layer 12M andthe mixed N-type organic semiconductor layer 14M, respectively, as inthe solar cells 109-111 shown in FIGS. 4A-4C, in order to increase thephotoelectric conversion efficiency. Of course, the buffer layer may beprovided in the top-type solar cells 106-111, similar to the bottom-typesolar cells 100-105.

For the mixed P-type organic semiconductor layer 12M, the P-type organicsemiconductor layer 12, the mixed N-type organic semiconductor layer14M, the N-type organic semiconductor layer 14, the substrate 15, theelectrode 16, the transparent electrode 18, the mixed layer 20, and thebuffer layer in this embodiment, the materials similar to one which isexplained in the first embodiment can be used, but the substrate 15 doesnot need to be transparent. Further, the solar cells 106-111 of thisembodiment can be produced with the method similar to one that isexplained in the first embodiment.

The materials and the structures of the solar cells 100-111 are notlimited to those in the above-mentioned embodiments. For example, anycomponent with the exception of organic semiconductor materials may beadded in appropriate amounts to a semiconductor layer such as the mixedP-type organic semiconductor layer 12M, the mixed N-type organicsemiconductor layer 14M, the P-type organic semiconductor layer 12, andthe N-type organic semiconductor layer 14. Further, two buffer layersmay be provided (namely, with one positioned between the transparentelectrode 18 and either the P-type organic semiconductor layer 12 or themixed P-type organic semiconductor layer 12M, and other positionedbetween either the N-type organic semiconductor layer 14 or the mixedN-type organic semiconductor layer 14M and the electrode 16; refer toFIGS. 1-4) as described above; however the buffer layer may be providedwith only one of these.

The method for producing the organic thin-film solar cell is not limitedto those shown in the above-mentioned embodiments. Namely, mixing theorganic semiconductor materials may be done by utilizing a method otherthan co-evaporation, and spin coating using the mixed solution. Forexample, the mixed P-type organic semiconductor layer 12M and the mixedN-type organic semiconductor layer 14M may be formed with ink-jet,gravure print, or others.

Moreover, the solar cells 100-111 can be made in a tandem structure. Forexample, in the above-mentioned solar cells 100-111 including at leastone of the mixed P-type organic semiconductor layer 12M and the mixedN-type organic semiconductor layer 14M, two or more layers of at leastone same layer-type of either P-type organic semiconductor layer 12,N-type organic semiconductor layer 14, mixed P-type organicsemiconductor layer 12M or mixed N-type organic semiconductor layer 14Mmay be stacked so as to form the tandem structure.

EXAMPLES

Next, the solar cell of this invention will be explained by Examples,but the present invention is not limited to these Examples.

Working Example 1

A thin-film (mixed P-type organic semiconductor layer 12M) having athickness of 20 nm was formed on the surface of the ITO (transparentelectrode 18) of a glass substrate patterned with ITO (thickness 0.7 mm,planar dimension 25 mm×25 mm, thickness of ITO 150 nm, manufactured bySanyo Vacuum Industries Co., Ltd.) using three P-type organicsemiconductor materials: CuPc (copper phthalocyanine), ZnPc (zincphthalocyanine) and TiOPc (titanyl Phthalocyanine) (all manufactured byOhjec Corporation); in equal amounts (molar number) by vacuum deposition(co-evaporation).

Moreover, a thin-film (N-type organic semiconductor layer 14) offullerene (expressed as “C60”) which is an N-type organic semiconductormaterial, having a thickness of 30 nm was formed on the mixed P-typeorganic semiconductor layer 12M by vacuum deposition. Next, an BCP layer(buffer layer) as a hole-blocking member having thickness of 10 nm wasformed on the N-type organic semiconductor layer 14 by vacuumdeposition, and then, a film of metal silver having thickness of 100 nmwas formed thereon as an electrode 16 by vacuum deposition. Finally,this multi-layer structure was sealed by a glass cap to obtain a solarcell of Working Example 1.

Comparative Example 1

A solar cell was manufactured in a manner similar to that in WorkingExample 1, except for using only CuPc as the P-type organicsemiconductor material in Comparative Example 1. The structures of thesolar cells in Working Example 1 and Comparative Example 1 are describedbriefly as follows.

Working Example 1 ITO/(CuPc+ZnPc+TiOPc) (20 nm)/C60 (30 nm)/BCP (10nm)/Ag (100 nm) Comparative Example 1 ITO/CuPc (20 nm)/C60 (30 nm)/BCP(10 nm)/Ag (100 nm)

In such a way, while the mixed P-type organic semiconductor layer 12Mwas formed using CuPc, ZnPc and TiOPc by co-evaporation in the solarcell of Working Example 1, the P-type organic semiconductor 12 wasformed from only CuPc in Comparative Example 1. Further, in both WorkingExample 1 and Comparative Example 1, the N-type organic semiconductor 14was formed using C60 only as the N-type organic semiconductor material.

Working Example 2

A thin-film (mixed P-type organic semiconductor layer 12M) having athickness of 20 nm was formed on the surface of the ITO (transparentelectrode 18) of a glass substrate which was the same as that in WorkingExample 1, using P-type organic semiconductor materials: CuPc and TiOPe(both manufactured by Ohjec Corporation) in equal amounts (molar number)by vacuum deposition (co-evaporation).

Moreover, a thin-film (mixed layer 20) having a thickness of 30 nm wasformed on the mixed P-type organic semiconductor layer 12M by vacuumdeposition (co-evaporation), using three materials, CuPc and TiOPc,which are the P-type organic semiconductor materials, and C60, which isthe N-type organic semiconductor material. In this case, the amounts ofCuPc, TiOPc and C60 were in CuPc:TiOPc C60=0.5:0.5:1 (molar ratio).Namely, the total amount (mole number) of P-type organic semiconductormaterials, CuPc and TiOPc, was made to be equal to that of the N-typeorganic semiconductor material, C60. Next, an N-type organicsemiconductor layer 14 utilizing only C60 as the N-type organicsemiconductor material, a BCP layer (buffer layer) and a film of anelectrode 16 of metal silver were formed on the mixed layer 20 and thensealed by a glass cap, similar to in Working Example 1. In such a way, asolar cell of Working Example 2 was obtained.

Comparative Example 2

A solar cell was manufactured in a manner similar to that in WorkingExample 2, except for using only CuPc as the P-type organicsemiconductor material and using CuPc and C60 of which amount (molarnumber) was the same as that of CuPc, as the ingredients of the mixedlayer 20, in Comparative Example 2. The structures of the solar cells ofWorking Example 2 and Comparative Example 2 are described briefly asfollows.

Working Example 2 ITO/(CuPc+TiOPc) (20 nm)/[(CuPc+TiOPc)+C60] (30nm)/C60 (30 nm)/BCP (10 nm)/Ag (100 nm) Comparative Example 2 ITO/CuPc(20 nm)/(CuPc+C60) (30 nm)/C60 (30 nm)/BCP (10 nm)/Ag (100 nm)

In such a way, while the mixed P-type organic semiconductor layer 12Mwas formed using CuPc and TiOPc by co-evaporation in the solar cell ofWorking Example 2, the P-type organic semiconductor 12 was formed fromonly CuPc in Comparative Example 2. Further, in Comparative Example 2,only CuPc was used as the P-type organic semiconductor material in themixed layer utilized in the P-type organic semiconductor layer.

Working Example 3

Aqueous dispersion of polythiophene conductive polymer PEDOT:PSS(manufactured by Bayer, product name: Baytron P) was applied onto thesurface of the ITO (transparent electrode 18) of a glass substrate,which was the same as that in Working Example 1, with spin coating andthen dried at 140° C. for 30 minutes so as to form a film having athickness of 50 nm as a buffer layer. Next, a chlorobenzene solution (4mass % of the total contents of P3HT and P3OT) in which P-type organicsemiconductor materials, P3HT (poly-3-hexylthiophene) and P3OT(poly-3-octylthiophene; both manufactured by Ohjec Corporation), weremixed in equal amounts (molar number) was applied onto the buffer layerwith spin coating and then dried at 150° C. for 10 minutes so that amixed P-type organic semiconductor layer 12M having a thickness of 50 nmwas formed.

Moreover, a chlorobenzene solution (4 mass % of the total contents ofP3HT, P3OT and PCBM) including P-type organic semiconductor materials,P3HT and P3OT, and an N-type organic semiconductor material, PCBM([6,6]-phenyl-C₆₁-butyric acid methyl ester), was applied onto the mixedP-type organic semiconductor layer 12M with spin coating and then driedat 150° C. for 10 minutes so that a thin-film (mixed layer 20) having athickness of 50 nm was formed. In this case, the amounts of P3HT, P3OTand PCBM were P3HT:P3OT:PCBM=0.5:0.5:1 (molar ratio). Namely, the totalamount of P-type organic semiconductor materials, P3HT and P3OT, wasmade to be equal (mole number) to that of the N-type organicsemiconductor material, PCBM. Next, a chlorobenzene solution of PCBM wasapplied onto the mixed layer 20 with spin coating and then dried at 150°C. for 10 minutes so that an N-type organic semiconductor layer 14having a thickness of 40 nm was formed. A film of metal aluminum, whichwas an electrode 16, was formed on the N-type organic semiconductorlayer 14 and then sealed by a glass cap. In this way, a solar cell ofWorking Example 3 was obtained.

Comparative Example 3

A solar cell was manufactured in a manner similar to that in WorkingExample 3, except for using only P3HT as the P-type organicsemiconductor material and using P3HT and PCBM of which the amount(molar number) was the same as that of P3HT, as the ingredients of themixed layer, in Comparative Example 3. The structures of the solar cellsin Working Example 3 and Comparative Example 3 are described briefly asfollows.

Working Example 3 ITO/PEDOT:PSS (50 nm)/(P3HT+P3OT) (50nm)/[(P3HT+P3OT)+PCBM] (50 nm)/PCBM (40 nm)/Al (100 nm) ComparativeExample 3 ITO/PEDOT:PSS (50 nm)/P3HT (50 nm)/(P3HT+PCBM) (50 nm)/PCBM(40 nm)/Al (100 nm)

In such a way, while the mixed P-type organic semiconductor layer 12Mwas formed of P3HT and P3OT in the solar cell of Working Example 3, theP-type organic semiconductor 12 was formed of P3HT only in ComparativeExample 3. Further, in Working Example 3 and Comparative Example 3, theingredients of the mixed layer were adjusted in accordance with thematerials of the P-type organic semiconductor layer.

Working Example 4

Aqueous dispersion of polythiophene conductive polymer, PEDOT:PSS(manufactured by Bayer, product name: Baytron P) was applied onto thesurface of the ITO (transparent electrode 18) of a glass substrate,which was the same as that in Working Example 1, with spin coating andthen dried at 140° C. for 30 minutes so as to form a film having athickness of 50 nm as a buffer layer. Next, a chlorobenzene solution (4mass % of the total contents of P3HT and MDMO-PPV) in which the P-typeorganic semiconductor materials, P3HT and MDMO-PPV(poly[2-methoxy-5-(3′,7′-dimethyloctyloxy) -1,4-phenylene vinylene]; allmanufactured by Ohjec Corporation), were mixed in equal amounts (molarnumber) were applied onto the buffer layer with spin coating and thendried at 150° C. for 10 minutes so that a mixed P-type organicsemiconductor layer 12M having a thickness of 50 nm was formed.

Moreover, a chlorobenzene solution (4 mass % of the total contents ofP3HT, MDMO-PPV and PCBM) including P-type organic semiconductormaterials, P3HT and MDMO-PPV, and an N-type organic semiconductormaterial, PCBM ([6,6]-phenyl-C₆₁-butyric acid methyl ester) was appliedonto the mixed P-type organic semiconductor layer 12M with spin coatingand then dried at 150° C. for 10 minutes so that a thin-film (mixedlayer 20) having a thickness of 80 nm was formed. In this case, theamounts of P3HT, MDMO-PPV and PCBM were P3HT: MDMO-PPVT: PCBM=0.5:0.5:1(molar ratio). Namely, the total amount of P-type organic semiconductormaterials, P3HT and MDMO-PPV, was made to be equal (mole number) to thatof N-type organic semiconductor material, PCBM. Next, a chlorobenzenesolution of PCBM (4 mass % contents) was applied onto the mixed layer 20with spin coating and then dried at 150° C. for 10 minutes so that anN-type organic semiconductor layer 14 having a thickness of 40 nm wasformed. Metal aluminum was formed into a film having a thickness of 120nm on the N-type organic semiconductor layer 14 as an electrode 16 withvacuum deposition and then sealed by a glass cap. In this way, a solarcell of Working Example 4 was obtained.

Comparative Example 4

A solar cell was manufactured in a manner similar to that in WorkingExample 4, except for using only P3HT as the P-type organicsemiconductor material and using P3HT and PCBM, of which the amount(molar number) was the same as that of P3HT, as the ingredients of themixed layer in Comparative Example 4. The structures of the solar cellsof Working Example 4 and Comparative Example 4 were described briefly asfollows.

Working Example 4 ITO/PEDOT:PSS(50 nm)/(P3HT+MDMO-PPV) (50nm)/[(P3HT+MDMO-PPV)+PCBM] (80 nm)/PCBM(40 nm)/Al (120 nm) ComparativeExample 4 ITO/PEDOT: PSS(50 nm)/P3HT (50 nm)/(P3HT+PCBM) (80 nm)/PCBM(40nm)/Al (120 nm) Working Example 5

Aluminum was vacuum-deposited on a glass substrate (thickness 0.7 mm,planar dimension 25 mm×25 mm) so as to form an anode 16 having athickness of 100 nm. A chlorobenzene solution of PCBM, which is anN-type organic semiconductor material, was applied onto the surface ofthe anode 16 with spin coating and then dried at 150° C. for 10 minutesso that an N-type organic semiconductor layer 14 having a thickness of40 nm was formed.

Moreover, a chlorobenzene solution (4 mass % of the total contents ofP3HT, P2HT and PCBM) including P-type organic semiconductor materials,P3HT and P3OT (both manufactured by Ohjec Corporation), and an N-typeorganic semiconductor material, PCBM was applied onto the N-type organicsemiconductor layer 14 with spin coating and then dried at 150° C. for10 minutes so that a thin-film (mixed layer 20) having a thickness of 80nm was formed. In this case, the amounts of P3HT, P2HT and PCBM wereP3HT: P3OT:PCBM=0.5:0.5:1 (molar ratio). Namely, the total amount of theP-type organic semiconductor materials, P3HT and P3OT, was made to beequal (mole number) to that of the N-type organic semiconductormaterial, PCBM.

Next, a chlorobenzene solution (4 mass % of the total contents of P3HTand P3OT), in which P-type organic semiconductor materials P3HT and P3OTwere mixed in equal amounts (molar number), was applied onto the mixedlayer 20 with spin coating and then dried at 150° C. for 10 minutes sothat a mixed P-type organic semiconductor layer 12M having a thicknessof 50 nm was formed.

Aqueous dispersion of polythiophene conductive polymer PEDOT:PSS(manufactured by Bayer, product name: Baytron P) was applied onto themixed P-type organic semiconductor layer 12M with spin coating and thendried at 140° C. for 30 minutes so as to form a layer of PEDOT: PSShaving a thickness of 50 nm, and then a layer of MoO₃ having a thicknessof 3 nm was provided thereon with a vacuum deposition method. The layerof PEDOT:PSS and the layer of MoO₃ are a buffer layers. A film of ITOwas formed on the layer of MoO₃ with sputtering, so as to forma film oftransparent electrode 18 having a thickness of 150 nm, and then sealedby a glass cap. In this way, a solar cell (top-type) of Working Example5 was obtained.

Comparative Example 5

A solar cell was manufactured in a manner similar to that in WorkingExample 5, except for using only P3HT as the P-type organicsemiconductor material and using P3HT and PCBM, of which the amount(molar number) was the same as that of P3HT, as the ingredients of themixed layer in Comparative Example 5. The structures of the solar cellsin Working Example 5 and Comparative Example 5 are described briefly asfollows.

Working Example 5 Al(100 nm)/PCBM(40 nm)/[(P3HT+P3OT)+PCBM] (80nm)/P3HT+P3OT(50 nm)/PEDOT : PSS (50 nm)/MoO₃ (3 nm)/ITO (150 nm)Comparative Example 5 Al(100 nm)/PCBM(40 nm)/(P3HT+PCBM) (80 nm)/P3HT(50nm)/PEDOT:PSS(50 nm)/MoO₃ (3 nm)/ITO(150 nm) Working Example 6

Silver was vacuum-deposited on a glass substrate (thickness 0.7 mm,planar dimension 25 mm×25 mm) so as to form an anode 16 having athickness of 100 nm. A BCP layer having thickness of 10 nm was formed asa hole-blocking member on the surface of the anode 16 with vacuumdeposition. An N-type organic semiconductor material, Fullerene (C60),was vacuum-deposited into a film on the BCP layer so as to form theN-type organic semiconductor layer 14 having a thickness of 30 nm. Next,a mixed P-type organic semiconductor layer 12M having a thickness of 20nm was formed on the N-type organic semiconductor layer 14 using threeP-type organic semiconductor materials, CuPc (copper phthalocyanine),ZnPc (zinc phthalocyanine) and TiOPc (titanyl Phthalocyanine) (allmanufactured by Ohjec Corporation) in equal amounts (molar number) byvacuum deposition. A layer of MoO₃ having thickness of 3 nm was formedon the mixed P-type organic semiconductor layer 12M with vacuumdeposition as a buffer layer. Next, a layer of ITO was formed on thelayer of MoO₃ with sputtering, so as to form a film of the transparentelectrode 18 having thickness of 150 nm and then sealed by a glass cap.In this way, a solar cell (top-type) of Working Example 6 was obtained.

Comparative Example 6

A solar cell was manufactured in a manner similar to that in WorkingExample 6, except for using CuPc only as the P-type organicsemiconductor material in Comparative Example 6. The structures of thesolar cells in Working Example 6 and Comparative Example 6 are describedbriefly as follows.

Working Example 6 Ag (100 nm)/BCP (10 nm)/C60 (30 nm)/CuPc+ZnPc+TiOPc(20nm)/MoO₃(3 nm)/ITO(150 nm) Comparative Example 6 Ag(100 nm)/BCP(10nm)/C60(30 nm)/CuPc(20 nm)/MoO₃ (3 nm)/ITO(150 nm)

Next, the performance of the solar cells of Working Examples 1-6 andComparative Examples 1-6 will be explained. The photoelectric conversionefficiency and so on were measured by irradiating a pseudo solar light(AM1.5) onto an effective device area of 5.25 mm² in the solar cells ofWorking Examples 1-6 and Comparative Examples 1-6 described above.Tables 1 and 2 show the results in this case. Further, the progress rateof the conversion efficiency was calculated by the following formulacomparing Working Example 1 and Comparative Example 1, Working Example 2and Comparative Example 2, Working Example 3 and Comparative Example 3,Working Example 4 and Comparative Example 4, Working Example 5 andComparative Example 5, and Working Example 6 and Comparative Example 6,respectively.

-   Progress Rate of Conversion Efficiency (%)={(Conversion Efficiency    in Working Example—Conversion Efficiency in Comparative    Example)/(Conversion Efficiency in Comparative Example)}×100

TABLE 1 Work. Comp. Work. Comp. Work. Comp. Ex. 1 Ex. 1 Ex. 2 Ex. 2 Ex.3 Ex. 3 Open Voltage 0.51 0.50 0.51 0.49 0.62 0.61 (V) Short-Circuit6.20 5.86 7.49 6.94 8.95 8.69 Current Density (mA/cm²) Fill Factor 0.470.45 0.48 0.45 0.41 0.41 Conversion 1.48 1.32 1.83 1.53 2.28 2.17Efficiency (%) Progress Rate of 12 — 20 — 5.1 — Conversion Efficiency(%)

TABLE 2 Work. Comp. Work. Comp. Work. Comp. Ex. 4 Ex. 4 Ex. 5 Ex. 5 Ex.6 Ex. 6 Open Voltage 0.65 0.61 0.45 0.43 0.49 0.45 (V) Short-Circuit8.45 8.21 7.40 6.87 5.46 5.22 Current Density (mA/cm²) Fill Factor 0.430.41 0.37 0.38 0.35 0.34 Conversion 2.36 2.05 1.23 1.12 0.94 0.81Efficiency (%) Progress Rate of 15 — 10 — 16 — Conversion Efficiency (%)

From these results, it was recognized that the solar cells of WorkingExamples 1-6 have better performance than the corresponding ComparativeExamples 1-6, respectively. The reason is that the short-circuit currentdensity was higher, so the photoelectric conversion efficiency wasbetter in all Working Examples compared to their correspondingComparative Examples, although no large differences regarding the openvoltage and the fill factor were shown. In detail, the photoelectricconversion efficiency was improved by 5% (comparison between WorkingExample 3 and Comparative Example 3) to 20% (comparison between WorkingExample 2 and Comparative Example 2).

The reasons why the solar cells of Working Examples 1-6, in accordancewith the above-mentioned embodiment, had the better photoelectricconversion efficiency as described above are as follows. In the Exampleof optical absorption spectrums of CuPc, ZnPc and TioPc (refer to FIG.5), the absorption band (absorption wavelength region) of TiOPc issubstantially different from those of CuPc and ZnPc. Accordingly, in theP-type organic semiconductor layer 12 formed from only one of CuPc, ZnPcor TioPc, a wavelength region of low absorbancy is present. For example,it is a long-wavelength region that is greater than or equal to 700 nmin the case of using CuPc or ZnPc only, or a wavelength region of550-600 nm in case of using TiOPc only.

Contrastingly, in the mixture in which CuPc, ZnPc and TiOPc, of whichthe optical absorption spectrums are different from each other, aremixed in equal amounts, the wavelength region of low absorbancy isreduced by overlapping their absorption regions. Accordingly, the solarlight can be absorbed more efficiently in the case of using such amixture, than in the case of using only one. This is obvious from theevidence of Working Example 1 using the mixture to form the mixed P-typeorganic semiconductor layer 12M displaying the higher photoelectricconversion efficiency than Comparative Example 1 using CuPc only.

Furthermore, the efficient electric generation can be achieved when themixed N-type organic semiconductor layer 14M is formed by selecting aplurality of organic semiconductor materials appropriately, as well asin the case of the mixed P-type organic semiconductor layer 12M.

As described above, selecting a plurality of proper organicsemiconductor materials, mixing these and then forming the mixed P-typeor N-type organic semiconductor layers 12M or 14M can increase thephotoelectric conversion efficiency of the solar cell, according to thepresent embodiments. Furthermore, the photoelectric conversionefficiency can be increased by only two layers, such as the mixed P-typeand mixed N-type organic semiconductor layers 12M and 14M and so on, andthe structure of solar cell becomes simpler than the case in which thephotoelectric conversion efficiency is improved by stacking a pluralityof P-type and N-type organic semiconductor layers comprising componentsthat are different from each other. This enables mass-production at lowcost of the solar cell having the excellent photoelectric conversionefficiency.

1. An organic thin-film solar cell comprising a P-type organicsemiconductor layer and an N-type organic semiconductor layer, at leastone of said P-type organic semiconductor layer and said N-type organicsemiconductor layer comprising a mixture of a plurality of organicsemiconductor materials of which absorption bands in an opticalabsorption spectrum are different from each other.
 2. The organicthin-film solar cell as claimed in claim 1, wherein a mixed layercomprising a mixture of a P-type organic semiconductor material and anN-type organic semiconductor material is further provided between saidP-type organic semiconductor layer and said N-type organic semiconductorlayer.
 3. The organic thin-film solar cell as claimed in claim 1,further comprising an electrode and a buffer layer, wherein said bufferlayer is provided between said electrode and an organic semiconductorlayer of at least one of said P-type organic semiconductor layer andsaid N-type organic semiconductor layer.
 4. The organic thin-film solarcell as claimed in claim 1, wherein said P-type organic semiconductorlayer includes polyphenylene vinylene, polyphenylene vinylenederivative, polythiophene, phthalocyanine, phthalocyanine derivative,porphyrin, pentacene, or rubrene as said organic semiconductor material.5. The organic thin-film solar cell as claimed in claim 1, wherein saidN-type organic semiconductor layer includes fullerene, fullerenederivative, carbon nanotube, or carbon nanotube derivative as saidorganic semiconductor material.
 6. The organic thin-film solar cell asclaimed in claim 1, wherein at least one of said P-type organicsemiconductor layer and said N-type organic semiconductor layer isplurally stacked.
 7. A method of producing an organic thin-film solarcell comprising a P-type organic semiconductor layer and an N-typeorganic semiconductor layer, comprising a step of forming at least oneof said P-type organic semiconductor layer and said N-type organicsemiconductor layer by mixing a plurality of organic semiconductormaterials.
 8. The organic thin-film solar cell as claimed in claim 2,further comprising an electrode and a buffer layer, wherein said bufferlayer is provided between said electrode and an organic semiconductorlayer of at least one of said P-type organic semiconductor layer andsaid N-type organic semiconductor layer.
 9. The organic thin-film solarcell as claimed in claim 2, wherein said P-type organic semiconductorlayer includes polyphenylene vinylene, polyphenylene vinylenederivative, polythiophene, phthalocyanine, phthalocyanine derivative,porphyrin, pentacene, or rubrene as said organic semiconductor material.10. The organic thin-film solar cell as claimed in claim 2, wherein saidN-type organic semiconductor layer includes fullerene, fullerenederivative, carbon nanotube, or carbon nanotube derivative as saidorganic semiconductor material.
 11. The organic thin-film solar cell asclaimed in claim 2, wherein at least one of said P-type organicsemiconductor layer and said N-type organic semiconductor layer isplurally stacked.
 12. The organic thin-film solar cell as claimed inclaim 3, wherein said P-type organic semiconductor layer includespolyphenylene vinylene, polyphenylene vinylene derivative,polythiophene, phthalocyanine, phthalocyanine derivative, porphyrin,pentacene, or rubrene as said organic semiconductor material.
 13. Theorganic thin-film solar cell as claimed in claim 3, wherein said N-typeorganic semiconductor layer includes fullerene, fullerene derivative,carbon nanotube, or carbon nanotube derivative as said organicsemiconductor material.
 14. The organic thin-film solar cell as claimedin claim 3, wherein at least one of said P-type organic semiconductorlayer and said N-type organic semiconductor layer is plurally stacked.15. The organic thin-film solar cell as claimed in claim 4, wherein saidN-type organic semiconductor layer includes fullerene, fullerenederivative, carbon nanotube, or carbon nanotube derivative as saidorganic semiconductor material.
 16. The organic thin-film solar cell asclaimed in claim 4, wherein at least one of said P-type organicsemiconductor layer and said N-type organic semiconductor layer isplurally stacked.
 17. The organic thin-film solar cell as claimed inclaim 5, wherein at least one of said P-type organic semiconductor layerand said N-type organic semiconductor layer is plurally stacked.